rc2014: another attempt at SIO autodetection

diff --git a/Kernel/platform-rc2014/rc2014.s b/Kernel/platform-rc2014/rc2014.s
index e5a31e9..1dbf0d9 100644 (file)
--- a/Kernel/platform-rc2014/rc2014.s
+++ b/Kernel/platform-rc2014/rc2014.s
@@ -87,19 +87,44 @@ init_hardware:
         out (FDC_DOR), a
 
        ; Play guess the serial port
-       ; This needs doing better. We might be fooled by floating flow
-       ; control lines as the SC104 does expose flow control. FIXME
-       in a,(SIOA_C)
-       and #0x2C
-       cp #0x2C
-       ; CTS and DCD should be high as they are not wired
-       jr nz, try_acia
+
+       ;
+       ; We are booted under ROMWBW, therefore use the same algorithm as
+       ; ROMWBW so if the probe fails we at least expect it to have failed
+       ; before we run.
+       ;
+       ; FIXME: see if we can cleanly ask ROMWBW for the device type
+       ;
+
+       ;
+       ; This could be the ACIA control port. If so we mash the settings
+       ; up but that is ok as we will port them back in the ACIA probe
+       ;
+
+       xor a
+       ld c,#SIOA_C
+       out (c),a                       ; RR0
+       in b,(c)                        ; Save RR0 value
+       inc a
+       out (c),a                       ; RR1
+       in a,(c)
+       cp b                            ; Same from both reads - not an SIO
+
+       jr z, try_acia
 
        ; Repeat the check on SIO B
-       in a,(SIOB_C)
-       and #0x2C
-       cp #0x2C
-       jr z, is_sio
+
+       xor a
+       ld c,#SIOB_C
+       out (c),a                       ; RR0
+       in b,(c)                        ; Save RR0 value
+       inc a
+       out (c),a                       ; RR1
+       in a,(c)
+       cp b                            ; Same from both reads - not an SIO
+
+       jr nz, is_sio
+
 try_acia:
        ;
        ;       Look for an ACIA